Postgres does not store the timezone information of TIMESTAMPTZ.
Instead it stores a UTC value and performs silent conversions
to the currently set timezone, when dealt with in the text format.
However this library bypasses the silent conversions
and communicates with Postgres using the UTC values directly.

Unlike in case of TIMESTAMPTZ,
Postgres does store the timezone information for TIMETZ.
However the Haskell's "time" library does not contain any composite type,
that fits the task, so we use a pair of TimeOfDay and TimeZone
to represent a value on the Haskell's side.